Construction methods for preventing land erosion and improving streams, or for revetments, and construction methods for preventing mountain landslides

ABSTRACT

Erosion or collapse of a stream or a river is prevented by mooring timber, stones, or the like with a longitudinal cable (steel cable) ( 1 ). Barrier-like members ( 3 ) such as timber and stones moored by using the longitudinal cable ( 1 ) are arranged substantially stepwise or parallel to each other on the ground near the eroded or collapsed place to prevent mountain landslides.

TECHNICAL FIELD

[0001] The present inventions relate to a method for simply andeffectively carrying out erosion preventive works, revetment works, orthe like for streams or rivers, without destroying the naturalenvironment of streams in mountains, other rivers, etc. These inventionsalso relate to a construction method for simply and effectivelystabilizing the ground surface on mountainsides without damaging thenatural environment.

BACKGROUND ART

[0002] The erosion or collapse of mountains and streams is caused by thedownward travel of earth and gravel produced upon the collapse ofmountains by mainly rainfall, snowfall, earthquakes, or the like,whereas erosion or collapse of ordinary rivers is caused mainly byfloods. However, because there are many techniques common to theprevention of these types erosions or collapses, mountain conservancywork techniques for preventing land erosion and improving streams andfor revetments conventionally applied to mountains or streams will bedescribed below.

[0003] Obviously, the best practice for preventing such erosion andcollapse and for restoration from such erosion and collapse is to makefull use of the water retention and mountainside-stabilizing ability offorests by covering a mountain with a forest, thereby perfecting amountainous and forested environment so as to permit prevention oralleviation of erosion and collapse of mountainsides and streams evenwhen a heavy rainfall or snowfall occurs.

[0004] However since very great costs and a long period of time arerequired to condition and maintain such a mountainous and forestedenvironment, many artificial works have been constructed at the sametime that efforts have been made to perfect the mountainous and forestedenvironments. These works are characterized in that an independentstructure is installed at a prescribed location in a mountainousdistrict, thereby it being attempted to reduce the velocity and quantityof flowing water, earth, and gravel by the effects of the weight of thestructure, or the bearing capacity of the bedrock and the likesupporting the structure. Installing a structure having these functionsrequires much material, labor, and costs. Their outlines are as follows(see Sadao Hagiwara, “Forest Water Utilization and Land-erosionPrevention” (Dendrology, Vol. 9), Asakura Publishing Co., 1953; andAritsune Takei, Ed., Land-erosion Preventive Engineering EibundoPublishing Co., 1993).

[0005] 1. Works for Streams

[0006] Cases of stream erosion are divided into downward erosion orvertical erosion, in which the depth of the stream bed is increased, andside erosion or horizontal erosion, in which the bank of the stream ishorizontally eroded. In the both cases, the banks of streams collapsedue to their own weight, leading to landslides or the like. As a result,huge quantities of earth and gravel accumulate on the stream bed. Earthand gravel that accumulate on the stream bed in large quantities arecarried by floodwaters, etc. downstream, and sometimes take the form ofmudflows having considerable destructive power and cause a great deal ofdamage to areas surrounding the downstream end. Works for streams areconstructed for the purpose of preventing such erosion, and restoringsuch eroded material, in streams, and more specifically, are classifiedinto the following categories (a) to (e).

[0007] (a) Soil-saving dam works

[0008] The long-established and most commonly used are the soil-savingdam (barrage) works. Works of this type have as their main objectpreventing downward erosion by providing a weir that runs perpendicularto a stream, and retaining gravel behind such a weir to make a newstream bed having a gentler slope, thereby reducing the power of theflowing water. A plurality of dams may be provided stepwise for a singlestream, depending on the inclination of the stream and the extent of theerosion. The materials and construction method used for installing thedam are selected in accordance with the strength required for the dam.The following kinds of dams have conventionally been built:

[0009] i. Stonemasonry dam

[0010] Wet masonry dam: using mortar

[0011] Dry masonry dam: using no mortar

[0012] Mixed masonry dam: using wet masonry for the main portions, anddry masonry for the other portions

[0013] ii. Concrete dam

[0014] iii. Wooden dam

[0015] iv. Wire cylinder dam

[0016] v. Plaited fence dam

[0017] (b) Works for groundsels

[0018] Works of this type have an object to maintain the currentcondition of a stream bed, whereby a bank of a stream is protected fromtributary washout. This is a work of solidifying a stream bed withstones, concrete, wire cylinders, plaited fences, mattresses (timberframes filled with stones), or the like.

[0019] (c) Revetment works

[0020] This is to provide a certain wall to protect a stream bed fromside erosion. Because this wall is made to be parallel with thewatercourse, it is known also as a longitudinal dike. These works usestones, concrete, wire cylinders, plaited fences, wooden fences, boards,or the like.

[0021] (d) Spur dikes

[0022] For the purpose of changing the direction of a watercoursecenter, a structure projecting with an appropriate length and in anappropriate direction from one shore or from both shores toward thecenter is made. Masonry or wire cylinders are employed.

[0023] (e) Watercourse works

[0024] These are watercourse alteration works for avoiding disturbancesthrough adjustment of watercourses or directing the watercourse from aweak shore to a stronger shore. A pitching, rubble, or concrete processis employed.

[0025] 2. Mountainside works

[0026] Works of this type are divided, in terms of the object, into twotypes, i.e., works for shaping an irregularly eroded area and works forground surface stabilization.

[0027] (a) Open cuts with sloping slides

[0028] These are works for shaping irregularly eroded ground (intotopographic features suitable for planting).

[0029] (b) Stage-making works

[0030] These are works for reducing the speed of runoff flowing on thesurface of the ground, and for promoting water absorption by the groundby providing stages on the open-cut mountainside. To protect the steepinclined surfaces on the fronts of the stages, the following processesare adopted:

[0031] Turing (using turf)

[0032] Simple terracing works (using Japanese pampas grass, Miscanthus)

[0033] Mountainside wicker works

[0034] Mountainside masonry works

[0035] (c) Works to cover mountainsides

[0036] These are works for preventing raindrops from hitting the groundby covering a mountainside made of earth, which has insufficientcohesive power. Thereby the velocity of runoff flowing on the surface ofthe ground is reduced. In these works the entire mountain is covered. Asspecific examples, works in which the mountainside is covered withbundles of fascine in a net shape should be noted.

[0037] (d) Works on mountainside watercourses

[0038] These are sodding works or works in which stones are pitched forprotecting a recess in a mountainside where water collects and flows.

[0039] 3. Landslide preventive works

[0040] These are culvert works and the like using fascine or wirecylinders filled with stones and gravel for the purpose of excludinggroundwater that may cause a landslide.

[0041] 4. Mudflow preventive works

[0042] (a) Soil-saving dam works

[0043] As described above

[0044] (b) Works for accumulating gravel

[0045] These are works for accumulating earth and gravel on an expandedportion of a stream watercourse. Thereby the force of a mudflow isreduced.

[0046] The conventional techniques for mountain and forest work asdescribed above have the following problems. For most of these problems,this is also the case with flood control works for ordinary rivers.

[0047] i. Needs of high costs and much labor

[0048] As described above, some mountain and forest work is alwaysrequired anywhere there is mountainous land, and for a single work, theobjective area to be covered by the work usually has a large expanse.Thus, when solid structures such as dams are to be constructed at manysites that are targeted, considerable labor, materials, and funds arerequired. With the limited financial capabilities of the nationalgovernment or local governments, sufficient work cannot be accomplished.In such a state, unless advances are made, the collapse of the nation'sland will continue due just to economic reasons.

[0049] 2. Difficulties of works and operations

[0050] In most cases sites for mountain and forest works are usuallynarrow places between mountains. There are therefore seriousdifficulties in building a solid structure by operating modemconstruction equipment and transport vehicles. Also, the risk to humanwelfare is very high.

[0051] 3. Necessity of expertise

[0052] Sophisticated expertise and special technology are required toinstall a structure to prevent continuous natural erosion and to permitrestoration of the eroded material. Even for, for example, constructinga dam, design and engineering based on scientific research and studies,and scientific knowledge, are necessary to determine at which site a damhaving a predetermined strength is to be constructed. For this purpose,it is inevitable to rely upon a special civil engineering company, andthere is almost no room to make full use of the knowledge and experienceof ordinary forestry workers.

[0053] 4. Difficulty in procuring materials for works

[0054] Construction of a dam requires materials such as steel products,aggregates, stones, and concrete in large quantities. It is difficult toprocure any of these materials locally, and it is therefore necessary totransport these materials over long distances from production areas.

[0055] 5. Non-flexibility of facilities

[0056] Once structures such as dams are built, they form solid fixedfacilities, and it is subsequently very difficult to modify, remove, orrelocate such facilities.

[0057] 6. Problems in environmental destruction caused by works

[0058] To construct a large-scale structure on mountainous land, it isnecessary to partially destroy the mountainous land or modify its shape.In many cases the natural environment of the land is damaged by such awork. Further, it is highly probable that such a structure will give afeeling of incompatibility with the land and damage the natural scenery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059]FIGS. 1 and 2 are schematic views for explaining a work on astream or a river and a structure for preventing land erosion andimproving a stream;

[0060]FIG. 3 is a schematic view for explaining a work for preventingerosion of a stream bed and a structure for preventing land erosion andimproving a stream;

[0061]FIG. 4 is a schematic view for explaining a work for a revetmentof a stream and a revetment structure;

[0062]FIG. 5 is a schematic view for explaining a work for stabilizingearth in a mountainside and a mountain-landslide-preventive structure;

[0063]FIG. 6 is a schematic view for explaining a work on a stream or ariver for preventing land erosion and improving a stream, and aland-erosion-preventive or stream-improving structure;

[0064]FIG. 7 is a schematic view explaining a work for preventingmountain landslides and a mountain-landslide-preventive structure; and

[0065]FIG. 8 is a schematic view for explaining a work on a stream or ariver for preventing land erosion and improving a stream, and aland-erosion-preventive or stream-improving structure.

DENOTATION OF REFERENCE NUMBERS

[0066] (1) Longitudinal cable

[0067] (2) Base point

[0068] (3) Barrier-like member

[0069] (4) Mooring cable

[0070] (5) Auxiliary cable

[0071] (6) Connecting cable

[0072] (7) Lateral cable

[0073] (8) Earth and gravel

[0074] (10) Stream or river

[0075] (20) Mountainside

[0076] (30) Mountain

DISCLOSURE OF THE INVENTIONS

[0077] Embodiment 1 of the present inventions relates to a constructionmethod for preventing land erosion and improving a stream, comprising:

[0078] (a) a step of directly or indirectly fixing at least onelongitudinal cable (1) to a base point (2); and

[0079] (b) a step of mooring at least two barrier-like members (3)directly by using said longitudinal cable (1) or by using a mooringcable (4) connected to said longitudinal cable (1), so that the at leasttwo barrier-like members (3) are provided in a stream or a riversubstantially perpendicular to the direction of the current of water atan appropriate interval in the direction from the upper end to the lowerend of the stream or river.

[0080] Embodiment 2 of the present inventions relates to a constructionmethod for preventing land erosion and improving a stream, comprising:

[0081] (a) a step of directly or indirectly fixing at least twolongitudinal cables (1) to a base point (2);

[0082] (b) a step of connecting said longitudinal cables (1) to eachother by the use of at least one lateral cable (7); and

[0083] (c) a step of mooring at least two barrier-like members (3)directly by using said longitudinal cables (1) and/or said lateral cable(7) or by using a mooring cable (4) connected to each longitudinal cable(1) and/or said lateral cable (7), so that the at least two barrier-likemembers (3) are provided in a stream or a river substantiallyperpendicular to the direction of the current of water at an appropriateinterval in the direction from the upper end to the lower end of thestream or river.

[0084] Embodiment 3 of the present inventions relates to a constructionmethod for a revetment, comprising:

[0085] (a) a step of directly or indirectly fixing at least onelongitudinal cable (1) to a base point (2); and

[0086] (b) a step of mooring at least one barrier-like member (3)directly by using said longitudinal cable (1) or by using a mooringcable (4) connected to said longitudinal cable (1), so that saidbarrier-like member (3) is provided in a stream or a river and along itsbank.

[0087] Embodiment 4-1 of the present inventions relates to aconstruction method for preventing mountain landslides, comprising:

[0088] (a) a step of directly or indirectly fixing at least onelongitudinal cable (1) to a base point (2) so as to provide thelongitudinal cable (1) on both sides of a mountain across a ridge of themountain; and

[0089] (b) a step of mooring at least two barrier-like members (3) foreach side of the mountain directly by using said longitudinal cable (1)or by using a mooring cable (4) connected to said longitudinal cable(1), so that the at least two barrier-like members (3) are provided oneach side of the mountain at an appropriate interval in the direction ofthe height of the mountain with the longer dimension of eachbarrier-like member (3) extending substantially at right angles to thedirection of the height of the mountain:

[0090] Embodiment 4-2 of the present inventions relates to aconstruction method for preventing mountain landslides, comprising:

[0091] (a) a step of directly or indirectly fixing at least onelongitudinal cable (1) to a base point (2); and

[0092] (b) a step of mooring at least two barrier-like members (3)directly by using said longitudinal cable (1) or by using a mooringcable (4) connected to said longitudinal cable (1), so that the at leasttwo barrier-like members (3) are provided at an appropriate interval inthe direction of the height of a mountain with the longer dimension ofeach barrier-like member (3) extending substantially at right angles tothe direction of the height of the mountain;

[0093] wherein said base point (2) is provided on a slope of themountain opposite the side of the mountain on which said barrier-likemembers (3) are provided and said longitudinal cable (1) is fixed acrossa ridge of the mountain; and

[0094] Embodiment 4-3 of the present inventions relates to aconstruction method for preventing mountain landslides, comprising:

[0095] (a) a step of directly or indirectly fixing at least onelongitudinal cable (1) to a base point (2) constituted by a cable thatis wound around a mountain; and

[0096] (b) a step of mooring at least two barrier-like members (3)directly by using said longitudinal cable (1) or by using a mooringcable (4) connected to said longitudinal cable (1), so that the at leasttwo barrier-like members (3) are provided at an appropriate interval inthe direction of the height of the mountain with the longer dimension ofeach barrier-like member (3) extending substantially at right angles tothe direction of the height of the mountain.

[0097] Embodiment 5-1 of the present inventions relates to aconstruction method for preventing mountain landslides, comprising:

[0098] (a) a step of directly or indirectly fixing at least twolongitudinal cables (1) to a base point (2) so as to provide thelongitudinal cables (1) on both sides of a mountain across a ridge ofthe mountain;

[0099] (b) a step of connecting said longitudinal cables (1) to eachother with at least one lateral cable (7); and

[0100] (c) a step of mooring at least two barrier-like members (3) foreach side of the mountain, directly by using said longitudinal cables(1) and/or said lateral cable (7) or by using a mooring cable (4)connected to each longitudinal cable (1) and/or said lateral cable (7),so that the at least two barrier-like members (3) are provided on eachside of the mountain at an appropriate interval in the direction of theheight of the mountain with the longer dimension of each barrier-likemember (3) substantially at right angles to the direction of the heightof the mountain;

[0101] Embodiment 5-2 of the present invention relates to a constructionmethod for preventing mountain landslides, comprising:

[0102] (a) a step of directly or indirectly fixing at least twolongitudinal cables (1) to a base point (2);

[0103] (b) a step of connecting said longitudinal cables (1) to eachother with at least one lateral cable (7); and

[0104] (c) a step of mooring at least two barrier-like members (3)directly by using said longitudinal cables (1) and/or said lateral cable(7) or by using a mooring cable (4) connected to each longitudinal cable(1) and/or said lateral cable (7), so that the at least two barrier-likemembers (3) are provided at an appropriate interval in the direction ofthe height of a mountain with the longer dimension of each barrier-likemember (3) substantially at right angles to the direction of the heightof the mountain;

[0105] wherein said base point (2) is provided on a slope of themountain opposite the side of the mountain on which said barrier-likemembers (3) are provided and said longitudinal cables (1) are fixedacross a ridge of the mountain; and

[0106] Embodiment 5-3 of the present inventions relates to aconstruction method for preventing mountain landslides comprising:

[0107] (a) a step of directly or indirectly fixing at least twolongitudinal cables (1) to a base point (2) constituted by a cable thatis wound around a mountain;

[0108] (b) a step of connecting said longitudinal cables (1) to eachother with at least one lateral cable (7); and

[0109] (c) a step of mooring at least two barrier-like members (3)directly by using said longitudinal cables (1) and/or said lateral cable(7) or by using a mooring cable (4) connected to each longitudinal cable(1) and/or said lateral cable (7), so that the at least two barrier-likemembers (3) are provided at an appropriate interval in the direction ofthe height of the mountain with the longer dimension of eachbarrier-like member (3) substantially at right angles to the directionof the height of the mountain.

[0110] Embodiment 6 of the present inventions relates to a constructionmethod for preventing land erosion and improving a stream, comprising:

[0111] (a) a step of directly or indirectly fixing a lateral cable (7)to at least two base points (2); and

[0112] (b) a step of mooring directly by using said lateral cable (7) orby using a mooring cable (4) connected to said lateral cable (7) atleast one barrier-like member (3) in a stream or a river so as to beprovided substantially perpendicular to the direction of the current ofwater;

[0113] wherein at least two sets of structures, each comprising saidlateral cable (7), the base points (2), and the barrier-like member (3)as essential components, are placed, so that said barrier-like members(3) are provided in the stream or river at an appropriate interval inthe direction from the upper end to the lower end of the stream orriver.

[0114] Embodiment 7 of the present inventions relates to aland-erosion-preventive or stream-improving structure, comprising:

[0115] at least one longitudinal cable (1), a base point (2), and atleast two barrier-like members (3), and further and optionally a mooringcable (4) and/or an auxiliary cable (5), wherein said longitudinal cable(1) is fixed to said base point (2) directly or indirectly via saidauxiliary cable (5), and wherein said barrier-like members (3) aremoored directly by using said longitudinal cable (1) or by using saidmooring cable (4) connected to said longitudinal cable (1), so that thebarrier-like members (3) are provided in a stream or a riversubstantially perpendicular to the direction of the current of water atan appropriate interval in the direction from the upper end to the lowerend of the stream or river.

[0116] Embodiment 8 of the present inventions relates to aland-erosion-preventive or stream-improving structure, comprising:

[0117] at least two longitudinal cables (1), a base point (2), at leastone lateral cable (7), and at least two barrier-like members (3), andfurther and optionally a mooring cable (4) and/or an auxiliary cable(5), wherein said longitudinal cables (1) are fixed to said base point(2) directly or indirectly via said auxiliary cable (5), and areconnected to each other with said lateral cable (7), and saidbarrier-like members (3) are moored directly by using said longitudinalcables (1) and/or said lateral cable (7), or by using said mooring cable(4) connected to each longitudinal cable (1) and/or said lateral cable(7), so that the barrier-like members (3) are provided in a stream orriver substantially perpendicular to the direction of the current ofwater at an appropriate interval in the direction from the upper end tothe lower end of the stream or river.

[0118] Embodiment 9 of the present inventions relates to a revetmentstructure comprising at least one longitudinal cable (1), a base point(2), and at least one barrier-like member (3), and further andoptionally a mooring cable (4) and/or an auxiliary cable (5), whereinsaid longitudinal cable (1) is fixed to said base point (2) directly orindirectly via said auxiliary cable (5), and said barrier-like members(3) are moored directly by using said longitudinal cable (1) or by usingsaid mooring cable (4) connected to said longitudinal cable (1), so thatsaid barrier-like members (3) are placed in a stream or river along itsbank.

[0119] Embodiment 10 of the present inventions relates to amountain-landslide-preventive structure, comprising:

[0120] at least one longitudinal cable (1), a base point (2), and atleast two barrier-like members (3), and further and optionally a mooringcable (4) and/or an auxiliary cable (5), wherein said longitudinal cable(1) is fixed to said base point (2) directly or indirectly via saidauxiliary cable (5) so as to provide the longitudinal cable (1) on bothsides of a mountain across a ridge of the mountain, and saidbarrier-like members (3) are moored directly by using said longitudinalcable (1) or by using said mooring cable (4) connected to saidlongitudinal cable (1), so that the barrier-like members (3) areprovided at an appropriate interval in the direction of the height ofthe mountain with their longer dimensions substantially at right anglesto the direction of the height of the mountain;

[0121] Embodiment 10-2 of the present inventions relates to amountain-landslide-preventive structure, comprising:

[0122] at least one longitudinal cable (1), a base point (2), and atleast two barrier-like members (3), and further and optionally a mooringcable (4) and/or an auxiliary cable (5), wherein said barrier-likemembers (3) are moored directly by using said longitudinal cable (1) orby using said mooring cable (4) connected to said longitudinal cable(1), so that the barrier-like members (3) are provided at an appropriateinterval in the direction of the height of the mountain with theirlonger dimensions substantially at right angles to the direction of theheight of the mountain, said base point (2) is provided on a slope ofthe mountain opposite the side of the mountain on which saidbarrier-like members (3) are provided, and said longitudinal cable (1)is fixed to said base point (2) directly or indirectly via saidauxiliary cable (5) across a ridge of the mountain; and

[0123] Embodiment 10-3 of the present inventions relates to amountain-landslide-preventive structure, comprising:

[0124] at least one longitudinal cable (1), a base point (2) constitutedby a cable that is wound around a mountain, and at least twobarrier-like members (3), and further and optionally a mooring cable(4), wherein said longitudinal cable (1) is fixed to said base point(2), and said barrier-like members (3) are moored directly by using saidlongitudinal cable (1) or by using said mooring cable (4) connected tosaid longitudinal cable (1), so that the barrier-like members (3) areprovided at an appropriate interval in the direction of the height ofthe mountain with their longer dimensions substantially at right anglesto the direction of the height of the mountain.

[0125] Embodiment 11-1 of the present inventions relates to amountain-landslide-preventive structure, comprising:

[0126] at least two longitudinal cables (1), a base point (2), at leastone lateral cable (7), and at least two barrier-like members (3), andfurther and optionally a mooring cable (4) and/or an auxiliary cable(5), wherein said longitudinal cables (1) are fixed to said base point(2) directly or indirectly via said auxiliary cable (5) so as to providethe longitudinal cables (1) on both sides of a mountain across a ridgeof the mountain and are connected to each other by said lateral cable(7), and said barrier-like members (3) are moored directly by using saidlongitudinal cables (1) and/or said lateral cable (7), or by using saidmooring cable (4) connected to each longitudinal cable (1) and/or saidlateral cable (7), so that the barrier-like members (3) are provided atan appropriate interval in the direction of the height of a mountainwith their longer dimensions substantially at right angles to thedirection of the height of the mountain;

[0127] Embodiment 11-2 of the present inventions relates to amountain-landslide-preventive structure, comprising:

[0128] at least two longitudinal cables (1), a base point (2), at leastone lateral cable (7), and at least two barrier-like members (3), andfurther and optionally a mooring cable (4) and/or an auxiliary cable(5), wherein said barrier-like members (3) are moored directly by usingsaid longitudinal cables (1) and/or said lateral cable (7), or by usingsaid mooring cable (4) connected to each longitudinal cable (1) and/orsaid lateral cable (7), so that the barrier-like members (3) areprovided at an appropriate interval in the direction of the height ofthe mountain with their longer dimensions substantially at right anglesto the direction of the height of the mountain, said base point (2) isprovided on a slope of the mountain opposite the side of the mountain onwhich said barrier-like members (3) are provided, and said longitudinalcables (1) are fixed to said base point (2) directly or indirectly viasaid auxiliary cable (5) across a ridge of the mountain and areconnected to each other by said lateral cable (7); and

[0129] Embodiment 11-3 of the present inventions relates to amountain-landslide-preventive structure comprising:

[0130] at least two longitudinal cables (1), a base point (2)constituted by a cable that is wound around a mountain, at least onelateral cable (7), and at least two barrier-like members (3), andfurther and optionally a mooring cable (4), wherein said longitudinalcables (1) are fixed to said base point (2) and are connected to eachother by said lateral cable (7), and said barrier-like members (3) aremoored directly by using said longitudinal cables (1) and/or saidlateral cable (7) or by using said mooring cable (4) connected to eachlongitudinal cable (1) and/or said lateral cable (7), so that thebarrier-like members (3) are provided at an appropriate interval in thedirection of the height of the mountain with their longer dimensionssubstantially at right angles to the direction of the height of themountain.

[0131] Embodiment 12 of the present inventions relates to aland-erosion-preventive or stream-improving structure comprising:

[0132] a lateral cable (7), at least two base points (2), and at leastone barrier-like member (3), and further and optionally a mooring cable(4) and/or an auxiliary cable (5), wherein said lateral cable (7) isfixed to said base points (2) directly or indirectly via said auxiliarycable (5), and said barrier-like member (3) is moored directly by usingsaid lateral cable (7) or by using said mooring cable (4) connected tosaid lateral cable (7), so as to be provided in a stream or a riversubstantially perpendicular to the direction of the current of water.

[0133] Specific embodiments of said construction method for preventingland erosion and improving a stream include one of or a combination oftwo or more of:

[0134] a) a case where the base point (2) is provided on land along thestream or river;

[0135] b) a case where the base point (2) is provided in the stream orriver;

[0136] c) a case where the base point (2) is a tree, a rock, or anartificial structure;

[0137] d) a case where said longitudinal cable (1) is directly fixed tosaid base point (2);

[0138] e) a case where said longitudinal cable (1) is indirectly fixedto said base point (2) via an auxiliary cable (5);

[0139] f) a case where said barrier-like members (3) are selected fromthe group consisting of a single piece of timber, bound timber, timberconnected in a venetian-blind shape, a concrete block, a wire cylinderfilled with stones, and a sandbag;

[0140] g) a case where said barrier-like members (3) are directly mooredby using said longitudinal cable (1) and/or lateral cable (7);

[0141] h) a case where said barrier-like members (3) are moored by usingsaid mooring cable (4);

[0142] i) a case where there are provided at least three barrier-likemembers (3), including at least two barrier-like members (3) which areplaced side-by-side and which may be connected to each other with aconnecting cable (6);

[0143] j) a case where the base point (2) is provided on any locationchosen from a slope of a mountain on the side where the stream or riveris located, a mountain ridge, and a slope of a mountain opposite theside where the stream or river is located;

[0144] k) a case where said lateral cable (7) is directly fixed to saidbase point (2);

[0145] l) a case where said lateral cable (7) is indirectly fixed tosaid base point (2) via an auxiliary cable (5); and

[0146] m) a case where at least one set of structures, each comprising alateral cable (7), a base point (2), and a barrier-like members (3) asessential components, comprise at least two barrier-like members (3)that are placed side-by-side and which may be connected to each otherwith said lateral cable (7).

[0147] Specific embodiments of said construction method for a revetmentinclude one of or a combination of two or more of:

[0148] a) a case where the base point (2) is provided on land along thestream or river;

[0149] b) a case where the base point (2) is provided in the stream orriver;

[0150] c) a case where the base point (2) is a tree, a rock, or anartificial structure;

[0151] d) a case where said longitudinal cable (1) is directly fixed tosaid base point (2);

[0152] e) a case where said longitudinal cable (1) is indirectly fixedto said base point (2) via an auxiliary cable (5);

[0153] f) a case where said barrier-like member (3) is selected from thegroup consisting of a single piece of timber, bound timber, timberconnected in a venetian-blind shape, a concrete block, a wire cylinderfilled with stones, and a sandbag;

[0154] g) a case where said barrier-like member (3) is directly mooredby using said longitudinal cable (1);

[0155] h) a case where barrier-like member (3) is moored by using saidmooring cable (4);

[0156] i) a case where there are provided at least two barrier-likemembers (3) which are connected to each other in series by a connectingcable (6); and

[0157] j) a case where the base point (2) is provided on any locationchosen from a slope of a mountain on the side where the stream or riveris located, a mountain ridge, and a slope of a mountain opposite theside where the stream or river is located.

[0158] Specific embodiments of said construction method for preventingmountain landslides include one of or a combination of two or more of:

[0159] a) a case where the base point (2) is a tree, a rock, or anartificial structure;

[0160] b) a case where said longitudinal cable (1) is directly fixed tosaid base point (2);

[0161] c) a case where said longitudinal cable (1) is indirectly fixedto said base point (2) via an auxiliary cable (5);

[0162] d) a case where said barrier-like members (3) are selected fromthe group consisting of a single piece of timber, bound timber, timberconnected in a venetian-blind shape, a concrete block, a wire cylinderfilled with stones, and a sandbag;

[0163] e) a case where said barrier-like members (3) are moored so as tobe provided stepwise on a mountainside;

[0164] f) a case where said barrier-like members (3) are directly mooredby using said longitudinal cable (1) and/or lateral cable (7);

[0165] g) a case where said barrier-like members (3) are moored by usingsaid mooring cable (4);

[0166] h) a case where on at least one side of a mountain there areprovided at least three barrier-like members (3), including at least twobarrier-like members (3) which are placed side-by-side and which may beconnected to each other with a connecting cable (6);

[0167] i) a case where said at least one barrier-like member (3) isprovided at each end of said longitudinal cable (1); and

[0168] j) a case where the base point (2) is further provided on amountain ridge.

[0169] The concept of the term “cable” as used in the present inventionsincludes a longitudinal cable (1), a mooring cable (4), an auxiliarycable (5), a connecting cable (6), and a lateral cable (7) in the firstto twelfth embodiments of the present inventions above, and furtherincludes other types of cables.

BEST MODE FOR CARRYING OUT THE INVENTION

[0170] The preferred embodiments of the present inventions will bedescribed below with reference to the drawings.

[0171]FIG. 1 is a schematic view for explaining a work on a stream or ariver for preventing land erosion and improving a stream, and aland-erosion-preventive or stream-improving structure.

[0172] In FIG. 1, a single longitudinal cable (1) is used. Thelongitudinal cable (1) is directly fixed to a base point (2) made ofconcrete installed in the stream. Barrier-like members (3 a, 3 b, 3 c)are connected to the longitudinal cable (1) via mooring cables (4). Inthis embodiment, three barrier-like members are used, and relative tothe barrier-like member (3 a), the barrier-like members (3 b) and (3 c)are positioned at an appropriate interval in the direction from theupper end to the lower end of the stream, i.e., in the direction thatthe water flows. The barrier-like members (3 b) and (3 c) are placedside-by-side. Further, the barrier-like members (3 a, 3 b and 3 c) aremoored substantially perpendicular to the direction of the current ofwater, i.e., with the longer dimension of them extending across theriver. As a result, the barrier-like members (3 b) and (3 c) arearranged substantially parallel to the barrier-like member (3 a) andform steps. In this embodiment, the barrier-like members (3 a, 3 b and 3c) are sandbags.

[0173]FIG. 2 is also a schematic view for explaining a work on a streamor a river for preventing land erosion and improving a stream, and aland-erosion-preventive or stream-improving structure.

[0174] In FIG. 2, two longitudinal cables (1) are used. The longitudinalcables (1) are fixed to base points (actually, trees) (2) via anauxiliary cable (5). The barrier-like members (3) consist of timber, andare directly moored by the longitudinal cables (1).

[0175]FIG. 3 is a schematic view for explaining a work and aland-erosion control structure for preventing erosion of a stream bed.

[0176] In FIG. 3, two longitudinal cables (1) are fixed tolarge-diameter standing trees (2) located outside the stream andconcrete blocks (2′) provided in the stream. That is, a standing treethat is naturally present on land along the inclined shore of the streamand concrete blocks, which are artificial structures, are used as basepoints (2 and 2′). In this case, when the individual base points (2 and2′) are not sufficiently solid, using more base points will suffice.According to the increasing length of a longitudinal cable (1), theresistance of the longitudinal cable (1) and the like to downward andsideward tension acting on the base points (2 and 2′) and thelongitudinal cable (1) increases. This increase in resistance is causedby the increase in the weight of the longitudinal cable (1) resultingfrom its greater length and the increase in general in the necessarynumber of the members of the base points (2), resulting in theresistance of the base points (2) being added to the above resistance.

[0177] In FIG. 3, timber, which is a natural product, is used as abarrier-like member (3). As shown in FIG. 3, the barrier-like members(3) may be moored so as to ride on the longitudinal cable (1) (themooring method for the two barrier-like members (3) that are providedupstream), or may be moored so as to run under the longitudinal cable(1) (the mooring method for the two barrier-like members that areprovided downstream). In the former case, the longitudinal cables (1)become more stable, while in the latter case, the barrier-like members(3) become more stable. Mooring cables (4) are used for mooring. At thelowest part of the river in that figure, each of the two barrier-likemembers (3) is moored by using each of the two longitudinal cables (1).In this case, a smaller (shorter in the longer dimension) barrier-likemember (3) can be used, Further, because a river has an increased widthtoward the downstream end, it may sometimes be necessary to place thebarrier-like members (3) side-by-side in the transverse direction so asto cope with the increased width of the river. In the embodiment shownin FIG. 3, the barrier-like members (3) that are placed side-by-side areconnected to each other with a connecting cable (6) to stabilize thebarrier-like members (3). About, for example, the moorage of the secondbarrier-like member (3) from the downstream side in FIG. 3, among theparts designated as mooring cables (4) in the above, the parts branchingfrom the longitudinal cable (1) to be two cables may be considered asparts of the longitudinal cable (1), and only the part that winds aroundthe timber may be considered as the mooring cable (4).

[0178] In the embodiment in FIG. 3, over time these barrier-like members(3) become capable of acting as a dam. Earth and gravel (8) are retainedupstream of these barrier-like members (3) to raise the stream bed toreduce the velocity of the water flow, thereby preventing thelongitudinal erosion of the stream bed. By accumulating earth and gravel(8), the barrier-like members (3) progressively become firmly secured atcertain positions, and thus their positional stability increases. Inthis embodiment, the effect of preventing longitudinal erosion is moreremarkable as the number of barrier-like members (3) is increased andthe intervals therebetween are reduced.

[0179]FIG. 4 is a schematic view for explaining a work for a revetmentof a stream and a revetment structure.

[0180] In FIG. 4, a single longitudinal cable (1) is fixed directly tobase points (actually, trees) (2) present on land outside a stream or bythe use of an auxiliary cable (5). The base points (2) are located alongthe eroded bank of the stream. The barrier-like members (3) are severalpieces of timber bound in a venetian-blind shape. In this embodiment,the barrier-like members (3) are moored to the longitudinal cable (1)via mooring cables (4), and are connected to each other in series byconnecting cables (6).

[0181] For the purpose of a revetment in this embodiment, thebarrier-like members (3) are moored so as to be along the shore of thestream, namely, with their longer dimensions parallel to the current.

[0182] By employing such a revetment work, earth and gravel accumulatearound the barrier-like members (3) to perform a function similar tothat of a weir, thus protecting the shore of the stream.

[0183]FIG. 5 is a schematic view for explaining a work for stabilizingearth in a mountainside and a mountain-landslide-preventive structure.

[0184] In FIG. 5, four longitudinal cables (1) are installed in such aform that each longitudinal cable (1) is fixed to several base points(2) on a wide and bare mountainside (20) suffering from increasingcollapse. The longitudinal cables (1) run across the mountain ridge (thepeak of the mountain) and extend to the opposite side (not shown) of themountain. Of course, base points (2) are also provided on the oppositeside of the mountain. That is, two base points (2) provided on the sitesnearest to the mountain top in FIG. 5 (one is shown in the figure, andthe other, which is provided on the opposite side of the mountain, isnot shown in this figure) are connected with the longitudinal cable (1),like loads that are arranged so as to be balanced. At need, base points(2) may also be provided on the mountain ridge. The distance between thelongitudinal cables (1) may be appropriately selected. Theselongitudinal cables (1) are connected to each other with lateral cables(7). A plurality of barrier-like members (3) are moored to thelongitudinal cables (1) and the lateral cables (7) via mooring cables(4). The barrier-like members (3) are connected to each other withconnecting cables (6) and placed side-by-side. As in this embodiment,the barrier-like members (3) are arranged with their longer dimensionsextending substantially at right angles to the direction of the heightof a mountain. The barrier-like member's (3) are placed on themountainside so as to be provided with appropriate intervals betweenthem, in the direction of the height of a mountain. It is not alwaysnecessary that all these intervals be equal. That is, as in thisembodiment, it is not always necessary that the barrier-like members (3)be regularly arranged stepwise. The collapse of earth and sand can alsobe inhibited to stabilize the mountainside by mooring as manybarrier-like members (3) as possible irregularly over the entiremountainside.

[0185] In the embodiment shown in FIG. 5, over time earth and sand areretained on the upper side of the barrier-like members (3) to stabilizethe mountainside (20), thus permitting planting, furling, or the like onthe thus stabilized mountainside (20).

[0186]FIG. 6 is a schematic view for explaining a work on a stream or ariver for preventing land erosion and improving a stream, and aland-erosion-preventive or stream-improving structure.

[0187] In the upstream side of the structure shown in FIG. 6, thelateral cable (7) is fixed to a tree (2) and a concrete block (2). Onthe other hand, in the structure in the downstream side, the lateralcable (7) is fixed to two trees (2). Because on the downstream sidethere are available trees (2) suitable for use as base points (2) atpositions that almost correspond to each other on both shores of thestream, the trees are used as the base points (2). In the upstream side,in contrast, no tree is available on one shore; a concrete block (2′) isplaced as a base point (2′) at an appropriate position on the shoreopposite to that having a tree (2). When no tree or the like suitablefor use as a base point (2) is available at an appropriate position, itis necessary to provide an artificial base point (2) as described above.However, when there are trees but their strengths are considered to beinsufficient, auxiliary cables (5) may be wound around a plurality oftrees on each shore, and lateral cables (7) may be connected to aposition where the auxiliary cables (5) are tied.

[0188] In this embodiment, concrete blocks (3) are used as barrier-likemembers (3), and are moored to lateral cables (7) by the use of mooringcables (4).

[0189] One of the technical ideas on which the present inventions arebased is to disperse the force acting on the barrier-like members andthe like when a mudflow, etc. occurs, by using a plurality ofbarrier-like members. As in the embodiment shown in FIG. 6, it istherefore necessary to provide a structure in which a plurality ofbarrier-like members are present in a stream or a river at anappropriate interval in the direction from the upper end to the lowerend, even when no longitudinal cable is used.

[0190]FIG. 7 is a schematic view for explaining a work for preventingmountain landslides and a mountain-land slide-preventive structure.

[0191] In the embodiment shown in FIG. 7, a cable (2) is wound aroundthe mountain near the mountain top (at about 80% of the distance fromthe bottom to the top of the mountain, for example) to serve as a basepoint (2). It is of course possible to connect the cable to base pointssuch as concrete blocks. In that case, the cable serves as an auxiliarycable for indirectly fixing longitudinal cables (1) to base points (2).

[0192] In the embodiment shown in FIG. 7, the longitudinal cables (1)are present only on a particular slope (mountainside) of the mountain(30). However, the longitudinal cables (1) may be provided over all theslopes of the mountain. The longitudinal cables (1) may be arranged atany appropriate intervals. The longitudinal cables (1) are connected toeach other via lateral cables (7). The positions of the lateral cables(7) are different between different rows having lateral cables (7). Byadopting this configuration, it is possible to cope flexibly with anyforce (load) irrespective of its direction, when a force caused by a Mowetc. acts on the structure of the present invention.

[0193] The barrier-like members (3) are connected to the lateral cables(7) via the mooring cables (4), and directly to the longitudinal cables(1).

[0194] In this embodiment also, over time earth and gravel are retainedat the upper side of the barrier-like members (3), to stabilize themountainside (20), thus permitting planting and furling thereafter.

[0195]FIG. 8 is a schematic view for explaining a work on a stream or ariver for preventing land erosion and improving a stream, and aland-erosion-preventive or stream -improving structure.

[0196] In the embodiment shown in FIG. 8, the longitudinal cables (1)mooring the barrier-like members (3) are connected to the base points(2) provided on the slope (mountainside) on which the mountain stream islocated, and further extend to the opposite side of the mountain (notshown), across the ridge of the mountain, to also be fixed by basepoints (2) provided on the slope of the opposite side.

[0197] The rest of the configuration is the same as in the embodimentshown in FIG. 2.

[0198] In the present invention, there is no particular limitationimposed on the material for the longitudinal cable (1). Any materialexhibiting a desired strength and excellent in water resistance may beused. An example is a steel cable. With the strength of steel cablesthat are now practically used, when timber, stones, or the like aremoored with such steel cables, and are fixed at appropriate sites, thereis no case where the steel cables are severed by a natural force, whichsevering results in a considerable displacement of the barrier-likemembers, or the barrier-like members in a large quantity flowingtogether over a short period. Various steel cables, including thosespecified in Japanese Industrial Standard G 3525, are available. Theirbreaking loads vary depending upon whether they are surface-treated,their types of twists used, their diameters, etc. An appropriate steelcable suitable for use may be selected, considering various conditionsat the installation site of the structures of the present inventions.Another example of a longitudinal cable (1) is a steel chain.

[0199] Particularly in the case of, for example, a construction work forpreventing mountain landslides of which the range of sites that are tobe worked is wide, the length of the steel cable can be freely adjustedas desired. Thus, the steel cable is suitable as a longitudinal cable(1) or a lateral cable (7). In this case, since there is no substantialdifficulty in covering the sites that are to be worked and this is asoft structure work (i.e., it is not always necessary to produce a solidconstruction), it is also possible to rapidly construct one at the siterequiring such a work. Further, in the case of a soft structure work,using steel cables also has other advantages, such as easy modification,repair, and relocation of an installed construction. When it is possibleto install a cable over a long span across a mountain ridge, it is notalways necessary that the individual base points have a very highstrength. Therefore, even when a work is conducted in a mountainous andisolated district, there is no serious difficulty.

[0200] As the base point (2), a tree, a rock, or an artificial structuresuch as a concrete block may be used.

[0201] When using a tree, it is not necessary that it be a big one, butit should have its roots fastened deep in the soil. If there areconcerns about the strength of a tree as a base point (2), a singlelongitudinal cable (1) may be fixed to two or more trees. Particularlyin a construction work for improving a stream or for a revetment along astream, trees are effective and applicable as base points (2).

[0202] When using an artificial structure for this purpose, the size andthe material may be appropriately selected according to the situation.In the construction work for preventing mountain landslides, there aresome cases in which trees alone may be insufficient to satisfy therequired number of base points (2), or in which no tree is present at anappropriate place. Therefore, it is recommended that base points (2)such as three-dimensional or circular pillar-shaped concrete blocks beprovided. On the other hand, when artificial structures are installed ina stream or a river to use as base points (2), concrete structures suchas Tetrapods (trademark) having a wave-breaking effect are preferablyused.

[0203] When the structure of the present invention is used forpreventing mountain landslides, a cable may be wound around the mountainat, for example, about 80% of the distance from the bottom to the top.Thus, the cable may serve as a base point (2).

[0204] For a land-erosion-preventive or stream-improving structure or astructure for a revetment, the base points (2) are provided on the shoreof or in the stream or the river. Additionally, a base point (2) may beprovided on the mountain slope on which the stream or river is locatedor on the ridge of the mountain, and the longitudinal cable (1) may beextended to reach the base point (2). Another preferred practice is toprovide a base point (2) on the slope opposite the side of the mountaincontaining the stream or river, and to extend the longitudinal cable (1)to this base point (2). A site where the ground is stable should befound on such an opposite side of the mountain. As a result, a firm basepoint (2) can be ensured.

[0205] For a mountain-landslide preventive structure also, it isdesirable to provide a base point (2) on a slope of the mountainopposite the mountainside having the barrier-like members (3) or, asrequired, on a mountain ridge, and to extend the longitudinal cable (1)to that base point (2).

[0206] Applicable barrier-like members (3) include timber, bound timber,timber connected in a venetian-blind shape, a concrete block, a wirecylinder filled with stones, particularly heavy stones, a sandbag, etc.

[0207] When barrier-like members (3) which are natural timber areinstalled separately or in combination stepwise at appropriate intervalson a stream bed suffering from serious erosion, using timber havingroots or branches makes it possible to increase the effect of retainingflowing water or earth and gravel. For a revetment also, using timberhaving branches or roots as a barrier-like member (3) is effective.

[0208] As barrier-like members (3) that are installed in the downstreamend of a stream or a river or near the piedmont, those having a longdimension are required when a single barrier-like member (3) is used. Itis therefore desirable to use two or more barrier-like members (3) thatare placed side-by-side. Additionally, the barrier-like members (3) arepreferably connected to each other via connecting cables (6). In thisarrangement, some earth and sand flows through the spaces between thebarrier-like members (3) and further onto the downstream (or piedmont)side. However because the force acting on the barrier-like members (3)is dispersed, the structures of the present inventions can be preventedfrom breaking.

[0209] When installing the structures of the present inventions for thepurpose of preventing a disaster caused by a collapse of a mountainside,it is another preferred practice to extend the longitudinal cable (1) onboth sides of the mountain, across the mountain ridge, and to moor thebarrier-like members (3) to both ends of the longitudinal cable (1).This permits coping with collapses within a wide range, or even out ofthe range of prediction, and effectively retaining earth, sand, and thelike by the effect of not only the base points (2), but also by theforce of the barrier-like members (3) provided on the side that has notcollapsed. In this case, as shown in FIG. 5, the base points (2) canalso be provided on just one side of the mountain, and the barrier-likemembers (3) may also be provided on only the side of the mountain wherethe base points (2) are not provided. In place of extending thelongitudinal cable (1) over the mountain peak, an auxiliary cable (5)may be fixed to the base points (2) so as to make a circle at the heightof about 80% of the distance from the bottom to the top of the mountain.Also, a plurality of longitudinal cables (1) may be connected to theauxiliary cable (5) to moor the barrier-like members (3) to the lowerends of the longitudinal cables (1). In place of extending thelongitudinal cable (1) over the mountain peak, an auxiliary cable (5)may be fixed to the base points (2) so as to make a circle at the heightof about 80% of the distance from the bottom to the top of the mountainAlso, a plurality of longitudinal cables (1) may be connected to theauxiliary cable (5) to moor the barrier-like members (3) to the lowerends of the longitudinal cables (1).

[0210] Although the materials for the mooring cable (4), the auxiliarycable (5), the connecting cable (6) and the lateral cable (7) are notparticularly limited, those that are the same as the material for thelongitudinal cable (1) are preferably used.

[0211] The longitudinal cable (1) or the auxiliary cable (5) may befixed to the base point (2) by any known method, such as winding it,fixing it by using metal fittings, or tying it. Connecting cables canalso be easily made by using, e.g., metal fittings usually used forconnecting steel cables. Mooring barrier-like members (3) by thelongitudinal cable (1) or the mooring cable (4) does not require aspecial method. It suffices to select a method for making fall use ofthe strength of the cable, and does not cause the barrier-like member(3) to flow toward the downstream end. The words “directly moored byusing the longitudinal cable (1)” as used herein mean that a mooringcable (4) is not used. This meaning does not therefore preclude usingsuch auxiliary tools such as metal fittings. Also, when using theauxiliary cable (4), auxiliary tools such as metal fittings can possiblybe used.

[0212] To transport barrier-like members (3) such as long and heavytimber for a long distance to relocate and arrange them at necessarypositions when employing the construction method of the presentinvention, the technology of gathering and transporting materials bymeans of any cabling commonly and presently used may be used.

[0213] Installing these cables and transporting and mooring, forexample, timber, do not require a special high-level technology.

[0214] The necessary strength of the structure of the present inventionvaries with the installation site. Generally, however, the strength isdetermined by considering weather conditions at the installation site,soil quality, and the velocity and rate of flow of the river. Anecessary strength is calculated by multiplying a value calculated onthe basis of known formula incorporating these various factors by, forexample, 1.2 (a safety factor of 20%).

[0215] One of the technical concepts of the present inventions is, asdescribed above, the dispersion of the force acting on the barrier-likemembers by the use of a plurality of them. However, the presentinventions do not preclude a structure having a single barrier-likemember. In the aforementioned embodiment shown in FIG. 6, each structurehas only a single barrier-like member. Other examples of the structuresof the present inventions having a single barrier-like member (not shownin figures) include:

[0216] (a) one based on a process comprising the steps of winding acable around a Tetrapod (trademark) serving as a base point (2) andbeing installed in a stream or a river to fix the cable to the Tetrapod(trademark), and winding the cable at its one unattached end around abarrier-like member (3) at a position near the center of thebarrier-like member (3), or winding the cable at both its unattachedends around a barrier-like member (3) at positions near both ends of thebarrier-like member (3), thus mooring one barrier-like member (3);

[0217] (b) one based on the steps of fixing one longitudinal cable (1)to one tree (a base point) and another longitudinal cable (1) to anothertree (a base point) located on one shore of a stream or a river, andmooring a barrier-like member (3) with these two longitudinal cables(1); and

[0218] (c) one in which a longitudinal cable (1) mooring a barrier-likemember (3) via a mooring cable (4) is fixed to a base point (2) providedon a mountainside (made of concrete, or a tree or a rock when anappropriate one is available).

[0219] A construction method comprising installing a plurality of suchstructures is also within the technical concepts of the presentinventions.

[0220] When the predicted value of a force acting on the barrier-likemembers (3) caused by a mudflow or the like occurring is small, just onestructure having only a single barrier-like member (3) may be installed.Such a construction method is within the scope of another technicalconcept of the present inventions.

Effects of the Inventions

[0221] The main materials used in the construction works for preventingland erosion and improving a stream, for revetments, and for preventingmountain landslides according to the present inventions are steelcables, and timber or stones obtained from mountains or rivers.

[0222] These materials are far more easily procurable compared withconventional materials for such works in terms of quantity as well ascost. Therefore, the present inventions have considerable economicmerits. Even when installing a steel cable over a long distance,large-scale work is not necessary if it is installed on the ground.

[0223] The methods of the present inventions are simple, and almost ofthem can be practiced by persons who do not have a special technicalknowledge, as work like common labor in a forest.

[0224] In this work, there is almost no risk of destroying the worksite, and there is only the slightest risk of damaging the scenery ofthe site. When natural timber and stones are used, environmentaldestruction via water pollution or the like is almost inconceivable,even after the natural timber and stones are buried or have decayed overa long period. Thus, in the present inventions a concept can beconsidered to be achieved in which the self-restoring power of nature isutilized and those resources coming from nature are returned to nature.That is, the present inventions not only protect nature by means of aforest (standing trees), but also cause the trees to play the role ofprotecting nature even after they are felled.

[0225] In the structures of the present inventions, the individualbarrier-like members have only a limited effect on land-erosionprevention and stream improvement, or on a revetment. However, in thepresent inventions, there is available an erosion-preventive effectequal to or even superior to a large scale artificial dam or a revetmentwork as a whole, merely by increasing the number of barrier-likemembers.

[0226] This dam function expected for work for a stream can also beexpected in other structures of the present inventions that aim atpreventing any extensive collapse of a mountainside where there isincreasing erosion and collapse. Other structures of the presentinventions are prepared by arranging on the mountainside natural timber,wire cylinders, or the like in a large quantity, and connecting andsecuring them by means of steel cables. These structures permit theexpectation that important functions of the mountainside will berestored over a relatively short period.

[0227] While a land-erosion-preventive and a stream improvement work ora revetment work using artificial structures such as concrete blocksseriously damages the precious natural landscape of scenic areas, theworks of the present inventions can be accomplished without usingconcrete blocks or the like, and the natural environment can bemaintained without damaging the landscape of the site.

[0228] By applying the methods of the present inventions, as describedabove, erosion of a stream, a river, or a mountainside on a huge scalecan be coped with.

[0229] In Japan about 19,000 sites are reported to have steep inclinesand to involve the risk of collapse, as of the end of March 1992. A 1993survey reported about 79,000 streams which have a probable risk ofmudflows and reported about 11,000 places exposed to a risk of alandslide (Mountain Conservancy Handbook, 1996 Edition, edited by theMountain Conservancy Institute; see page 23). For fiscal 1995 (April1995 through March 1996), Japan had a total budget for mountainconservancy operations of about 453 billion yen (Mountain ConservancyHandbook, 1996 Edition; see page 87).

[0230] For ordinary rivers also, the number of sites requiring aland-erosion-preventive or stream-improvement work or a revetment workand the budget for this purpose are considered to be almost on the samelevel as above.

[0231] Practice of the present inventions is far easier than theconventional methods as described above, and does not require huge costsfor the work. Therefore, the range and sites of work for the preventionof erosion and collapse and restoration from such erosion and collapsein the natural land, particularly including mountainous lands, involvingthe above-mentioned risks, can therefore be greatly expanded. In thepresent inventions, timber and stones are the main materials. This meansthat mountain conservancy effects can be improved by the effective useof trees that have fallen because of wind, timber from culling, andearth and gravel from streams in large quantities, which to date havebeen of only limited economic value. By applying the present inventionsto land erosion prevention, stream improvements, or revetments ofordinary rivers, safe rivers that are made with their natural scenerybeing considered, and which differ from conventional ones, which aremade with Just their efficiency being considered, disregarding thenatural environment, such as when a concrete structure is used, areachievable. Further, the present inventions provide general forestryworkers with a considerable opportunity for employment, thus makingcontributions possible to stimulate farming and forestry villages.Application of the present inventions furthermore makes it possible, byartificial means, to prevent even large-scale erosion or collapse ofmountainous land, and to restore it from such erosion or collapse, whichhas so far been believed to be almost impossible. To be more exact, eventhe dream of preventing the erosion of Mount Fuji may come true. Sucheffects of the present inventions are thus very remarkable.

What is claimed is:
 1. A construction method for preventing land erosionand improving a stream, comprising: (a) a step of directly or indirectlyfixing at least one longitudinal cable (1) to a base point (2); and (b)a step of mooring at least two barrier-like members (3) directly byusing said longitudinal cable (1) or by using a mooring cable (4)connected to said longitudinal cable (1), so that the at least twobarrier-like members (3) are provided in a stream or a riversubstantially perpendicular to the direction of the current of water atan appropriate interval in the direction from the upper end to the lowerend of the stream or river.
 2. The construction method for preventingland erosion and improving a stream according to claim 1 , wherein thebase point (2) is provided on land along the stream or river.
 3. Theconstruction method for preventing land-erosion and improving a streamaccording to claim 1 , wherein the base point (2) is provided in thestream or river.
 4. The construction method for preventing land erosionand improving a stream according to claim 1 , wherein the base point (2)is a tree, a rock, or an artificial structure.
 5. The constructionmethod for preventing land erosion and improving a stream according toclaim 1 , wherein said longitudinal cable (1) is directly fixed to saidbase point (2).
 6. The construction method for preventing land erosionand improving a stream according to claim 1 , wherein said longitudinalcable (1) is indirectly fixed to said base point (2) via an auxiliarycable (5).
 7. The construction method for preventing land erosion andimproving a stream according to claim 1 , wherein said barrier-likemembers (3) are selected from the group consisting of a single piece oftimber, bound timber, timber connected in a venetian-blind shape, aconcrete block, a wire cylinder filled with stones, and a sandbag. 8.The construction method for preventing land erosion and improving astream according to claim 1 , wherein said barrier-like members (3) aredirectly moored by using said longitudinal cable (1).
 9. Theconstruction method for preventing land erosion and improving a streamaccording to claim 1 , wherein said barrier-like members (3) are mooredby using said mooring cable (4).
 10. The construction method forpreventing land erosion and improving a stream according to claim 1 ,wherein at least three barrier-like members (3) are provided, includingat least two barrier-like members (3) that are placed side-by-side andwhich may be connected to each other with a connecting cable (6).
 11. Aconstruction method for preventing land erosion and improving a stream,comprising: (a) a step of directly or indirectly fixing at least twolongitudinal cables (1) to a base point (2); (b) a step of connectingsaid longitudinal cables (1) to each other by the use of at least onelateral cable (7); and (c) a step of mooring at least two barrier-likemembers (3) directly by using said longitudinal cables (1) and/or saidlateral cable (7) or by using a mooring cable (4) connected to eachlongitudinal cable (1) and/or said lateral cable (7), so that the atleast two barrier-like members (3) are provided in a stream or a riversubstantially perpendicular to the direction of the current of water atan appropriate interval in the direction from the upper end to the lowerend of the stream or river.
 12. The construction method for preventingland erosion and improving a stream according to claim 11 , wherein saidbarrier-like members (3) are directly moored by using said longitudinalcables (1) and/or said lateral cable (7).
 13. A construction method fora revetment, comprising: (a) a step of directly or indirectly fixing atleast one longitudinal cable (1) to a base point (2); and (b) a step ofmooring at least one barrier-like member (3) directly by using saidlongitudinal cable (1) or by using a mooring cable (4) connected to saidlongitudinal cable (1), so that said barrier-like member (3) is providedin a stream or a river and along its bank.
 14. The construction methodfor a revetment according to claim 13 , wherein the base point (2) isprovided on land along the stream or river.
 15. The construction methodfor a revetment according to claim 13 , wherein the base point (2) isprovided in the stream or river.
 16. The construction method for arevetment according to claim 13 , wherein the base point (2) is a tree,a rock, or an artificial structure.
 17. The construction method for arevetment according to claim 13 , wherein said longitudinal cable (1) isdirectly fixed to said base point (2).
 18. The construction method for arevetment according to claim 13 , wherein said longitudinal cable (1) isindirectly fixed to said base point (2) via an auxiliary cable (5). 19.The construction method for a revetment according to claim 13 , whereinsaid barrier-like member (3) is selected from the group consisting of asingle piece of timber, bound timber, timber connected in avenetian-blind shape, a concrete block, a wire cylinder filled withstones, and a sandbag.
 20. The construction method for a revetmentaccording to claim 13 , wherein said barrier-like member (3) is directlymoored by using said longitudinal cable (1).
 21. The construction methodfor a revetment according to claim 13 , wherein said barrier-like member(3) is moored by using said mooring cable (4).
 22. The constructionmethod for a revetment according to claim 13 , wherein there areprovided at least two barrier-like members (3) connected in series toeach other with a connecting cable (6).
 23. A construction method forpreventing mountain landslides, comprising: (a) a step of directly orindirectly fixing at least one longitudinal cable (1) to a base point(2) so as to provide the longitudinal cable (1) on both sides of amountain across a ridge of the mountain; and (b) a step of mooring atleast two barrier-like members (3) directly by using said longitudinalcable (1) or by using a mooring cable (4) connected to said longitudinalcable (1), 50 that the at least two barrier-like members (3) areprovided on each side of the mountain at an appropriate interval in thedirection of the height of a mountain with the longer dimension of eachbarrier-like member (3) extending substantially at right angles to thedirection of the height of the mountain.
 24. The construction method forpreventing mountain landslides according to claim 23 , wherein said basepoint (2) is a tree, a rock, or an artificial structure.
 25. Theconstruction method for preventing mountain landslides according toclaim 23 , wherein said longitudinal cable (1) is directly fixed to saidbase point (2).
 26. The construction method for preventing mountainlandslides according to claim 23 , wherein said longitudinal cable (1)is indirectly fixed to said base point (2) via an auxiliary cable (5).27. The construction method for preventing mountain landslides accordingto claim 23 , wherein said barrier-like members (3) are selected fromthe group consisting of a single piece of timber, bound timber, timberconnected in a venetian-blind shape, a concrete block, a wire-cylinderfilled with stones, and a sandbag.
 28. The construction method forpreventing mountain landslides according to claim 23 , wherein saidbarrier-like members (3) are moored so that they are provided stepwiseon a mountainside.
 29. The construction method for preventing mountainlandslides according to claim 23 , wherein said barrier-like members (3)are directly moored by using said longitudinal cable (1).
 30. Theconstruction method for preventing mountain landslides according toclaim 23 , wherein said barrier-like members (3) are moored by usingsaid mooring cable (4).
 31. The construction method for preventingmountain landslides according to claim 23 , wherein on at least one sideof the mountain, at least three barrier-like members (3) are provided,including at least two barrier-like members (3) which are placedside-by-side and which may be connected to each other with a connectingcable (6).
 32. The construction method for preventing mountainlandslides according to claim 31 , wherein at least one barrier-likemember (3) is provided at each end of said longitudinal cable (1).
 33. Aconstruction method for preventing mountain landslides, comprising: (a)a step of directly or indirectly fixing at least two longitudinal cables(1) to a base point (2); (b) a step of connecting said longitudinalcables (1) to each other with at least one lateral cable (7); (c) a stepof mooring at least two barrier-like members (3) directly by using saidlongitudinal cables (1) and/or said lateral cable (7) or by using amooring cable (4) connected to each longitudinal cable (1) and/or saidlateral cable (7), so that the at least two barrier-like members (3) areprovided at an appropriate interval in the direction of the height of amountain with the longer dimension of each barrier-like member (3)substantially at right angles to the direction of the height of themountain; and wherein said base point (2) is provided on a slopeopposite the side of the mountain on which said barrier-like members (3)are provided, and said longitudinal cables (1) are fixed to said basepoint (2) across a ridge of the mountain.
 34. A construction method forpreventing land erosion and improving a stream, comprising: (a) a stepof directly or indirectly fixing a lateral cable (7) to at least twobase points (2); and (b) a step of mooring directly by using saidlateral cable (7) or by using a mooring cable (4) connected to saidlateral cable (7) at least one barrier-like member (3) in a stream or ariver so as to be provided substantially perpendicular to the directionof the current of water; wherein at least two sets of structures, eachcomprising said lateral cable (7), the base points (2), and thebarrier-like member (3) as essential components, are placed, so thatsaid barrier-like members (3) are provided in the stream or river at anappropriate interval in the direction from the upper end to the lowerend of the stream or river.
 35. The construction method for preventingland erosion and improving a stream according to claim 34 , wherein saidlateral cable (7) is directly fixed to said base points (2).
 36. Theconstruction method for preventing land erosion and improving a streamaccording to claim 34 , wherein said lateral cable (7) is indirectlyfixed to said base points (2) via an auxiliary cable (5).
 37. Theconstruction method for preventing land erosion and improving a streamaccording to claim 34 , wherein said barrier-like member (3) is directlymoored by using said lateral-cable (7).
 38. The construction method forpreventing land erosion and improving a stream according to claim 34 ,wherein at least one set of said structures comprises at least twobarrier-like members (3) which are placed side-by-side and which may beconnected to each other with a connecting cable (6).
 39. Aland-erosion-preventive or site am-imp roving structure comprising atleast one longitudinal cable (1), a base point (2), and at least twobarrier-like members (3), and further and optionally a mooring cable (4)and/or an auxiliary cable (5), wherein said longitudinal cable (1) isfixed to said base point (2) directly or indirectly via said auxiliarycable (5), and wherein said barrier-like members (3) are moored directlyby using said longitudinal cable (1) or by using said mooring cable (4)connected to said longitudinal cable (1), so that the barrier-likemembers (3) are provided in a stream or a river substantiallyperpendicular to the direction of the current of water at an appropriateinterval in the direction from the upper end to the lower end of thestream or river.
 40. A land-erosion-preventive or stream-imp rovingstructure comprising at least two longitudinal cables (1), a base point(2), at least one lateral cable (7), and at least two barrier-likemembers (3), and further and optionally a mooring cable (4) and/or anauxiliary cable (5), wherein said longitudinal cables (1) are fixed tosaid base point (2) directly or indirectly via said auxiliary cable (5),and are connected to each other with said lateral cable (7), and saidbarrier-like members (3) are moored directly by using said longitudinalcables (1) and/or said lateral cable (7), or by using said mooring cable(4) connected to each longitudinal cable (1) and/or said lateral cable(7), so that the barrier-like members (3) are provided in a stream orriver substantially perpendicular to the direction of the current ofwater at an appropriate interval in the direction from the upper end tothe lower end of the stream or river.
 41. A revetment structurecomprising at least one longitudinal cable (1), a base point (2), and atleast one barrier-like member (3), and further and optionally a mooringcable (4) and/or an auxiliary cable (5), wherein said longitudinal cable(1) is fixed to said base point (2) directly or indirectly via saidauxiliary cable (5), and said barrier-like members (3) are mooreddirectly by using said longitudinal cable (1) or by using said mooringcable (4) connected to said longitudinal cable (1), so that saidbarrier-like members (3) are placed in a stream or river and along itsbank.
 42. A mountain-landslide-preventive structure comprising at leastone longitudinal cable (1), a base point (2), and at least twobarrier-like members (3), and further and optionally a mooring cable (4)and/or an auxiliary cable (5), wherein said longitudinal cable (1) isfixed to said base point (2) directly or indirectly via said auxiliarycable (5) so as to provide the longitudinal cable (1) on both sides of amountain across a ridge of the mountain, and said barrier-like members(3) are moored directly by using said longitudinal cable (1) or by usingsaid mooring cable (4) connected to said longitudinal cable (1), 50 thatthe barrier-like members (3) are provided at an appropriate interval inthe direction of the height of a mountain with their longer dimensionssubstantially at right angles to the direction of the height of themountain.
 43. A mountain-landslide-preventive structure comprising atleast two longitudinal cables (1), a base point (2), at least onelateral cable (7), and at least two barrier-like members (3), andfurther and optionally a mooring cable (4) and/or an auxiliary cable(5), wherein said longitudinal cables (1) are fixed to said base point(2) directly or indirectly via said auxiliary cable (5) so as to providethe longitudinal cables (1) on both sides of a mountain across a ridgeof the mountain, and are connected to each other with said lateral cable(7), and said barrier-like members (3) are moored directly by using saidlongitudinal cables (1) and/or said lateral cable (7) or by using saidmooring cable (4) connected to each longitudinal cable (1) and/or saidlateral cable (7), so that the barrier-like members (3) are provided atan appropriate interval in the direction of the height of a mountainwith their longer dimensions substantially at right angles to thedirection of the height of the mountain.
 44. A land-erosion-preventiveor stream-improving structure comprising a lateral cable (7), at leasttwo base points (2), and at least one barrier-like member (3), andfurther and optionally a mooring cable (4) and/or an auxiliary cable(5), wherein said lateral cable (7) is fixed to said base points (2)directly or indirectly via said auxiliary cable (5), and saidbarrier-like member (3) is moored directly by using said lateral cable(7) or by using said mooring cable (4) connected to said lateral cable(7), so as to be provided in a stream or a river substantiallyperpendicular to the direction of the current of water.
 45. Theconstruction method for preventing land erosion and improving a streamaccording to claim 1 , wherein the base point (2) is provided on anylocation chosen from a slope of a mountain on the side where the streamor river is located, a mountain ridge, and a slope of a mountainopposite the side where the stream or river is located.
 46. Theconstruction method for preventing land erosion and improving a streamaccording to claim 13 , wherein the base point (2) is provided on anylocation chosen from a slope of a mountain on the side where the streamor river is located, a mountain ridge, and a slope of a mountainopposite the side where the stream or river is located.
 47. Aconstruction method for preventing mountain landslides, comprising: (a)a step of directly or indirectly fixing at least one longitudinal cable(1) to a base point (2); and (b) a step of mooring at least twobarrier-like members (3) directly by using said longitudinal cable (1)or by using a mooring cable (4) connected to said longitudinal cable(1), so that the at least two barrier-like members (3) are provided atan appropriate interval in the direction of the height of a mountainwith the longer dimension of each barrier-like member (3) extendingsubstantially at right angles to the direction of the height of themountain; wherein said base point (2) is located on a slope of themountain opposite the side of the mountain where said barrier-likemembers (3) are provided, and said longitudinal cable (1) is fixed tosaid base point (2) so that the cable (1) extends across a ridge of themountain.
 48. The construction method for preventing mountain landslidesaccording to claim 47 , wherein a base point (2) is additionallyprovided on the ridge of the mountain.
 49. A construction method forpreventing mountain landslides, comprising: (a) a step of directly orindirectly fixing at least one longitudinal cable (1) to a base point(2) constituted by a cable that is wound around a mountain; and (b) astep of mooring at least two barrier-like members (3) directly by usingsaid longitudinal cable (1) or by using a mooring cable (4) connected tosaid longitudinal cable (1), so that the at least two barrier-likemembers (3) are provided at an appropriate interval in the direction ofthe height of the mountain with the longer dimension of eachbarrier-like member (3) extending substantially at right angles to thedirection of the height of the mountain.
 50. A construction method forpreventing mountain landslides, comprising: (a) a step of directly orindirectly fixing at least two longitudinal cables (1) to a base point(2) so as to provide the longitudinal cables (1) on both sides of amountain across a ridge of the mountain; (b) a step of connecting saidlongitudinal cables (1) to each other with at least one lateral cable(7); and (c) a step of mooring at least two barrier-like members (3) foreach side of the mountain directly by using said longitudinal cables (1)and/or said lateral cable (7) or by using a mooring cable (4) connectedto each longitudinal cable (1) and/or said lateral cable (7), so thatthe at least two barrier-like members (3) are provided on each side ofthe mountain at an appropriate interval in the direction of the heightof the mountain with the longer dimension of each barrier-like member(3) substantially at right angles to the direction of the height of themountain.
 51. The construction method for preventing mountain landslidesaccording to claim 50 , wherein said barrier-like members (3) are mooreddirectly by using said longitudinal cables (1) and/or said lateral cable(7).
 52. A construction method for preventing mountain landslides,comprising: (a) a step of directly or indirectly fixing at least twolongitudinal cables (1) to a base point (2) constituted by a cable thatis wound around a mountain; (b) a step of connecting said longitudinalcables (1) to each other with at least one lateral cable (7); and (c) astep of mooring at least two barrier-like members (3) directly by usingsaid longitudinal cables (1) and/or said lateral cable (7) or by using amooring cable (4) connected to each longitudinal cable (1) and/or saidlateral cable (7), so that the at least two barrier-like members (3) areprovided at an appropriate interval in the direction of the height ofthe mountain with the longer dimension of each barrier-like member (3)substantially at right angles to the direction of the height of themountain.
 53. A mountain-landslide-preventive structure comprising atleast one longitudinal cable (1), a base point (2), and at least twobarrier-like members (3), and further and optionally a mooring cable (4)and/or an auxiliary cable (5), wherein said barrier-like members (3) aremoored directly by using said longitudinal cable (1) or by using saidmooring cable (4) connected to said longitudinal cable (1), so that thebarrier-like members (3) are provided at an appropriate interval in thedirection of the height of a mountain with their longer dimensionssubstantially at right angles to the direction of the height of themountain, said base point (2) is provided on a slope of the mountainopposite the side of the mountain on which said barrier-like members (3)are provided, and said longitudinal cable (1) is fixed to said basepoint (2) directly or indirectly via said auxiliary cable (5) across aridge of the mountain.
 54. A mountain-landslide-preventive structurecomprising at least one longitudinal cable (1), a base point (2)constituted by a cable that is wound around a mountain, and at least twobarrier-like members (3), and further and optionally a mooring cable(4), wherein said longitudinal cable (1) is fixed to said base point(2), and said barrier-like members (3) are moored directly by using saidlongitudinal cable (1) or by using said mooring cable (4) connected tosaid longitudinal cable (1), 50 that the barrier-like members (3) areprovided at an appropriate interval in the direction of the height ofthe mountain with their longer dimensions substantially at right anglesto the direction of the height of the mountain.
 55. Amountain-landslide-preventive structure comprising at least twolongitudinal cables (1), a base point (2), at least one lateral cable(7), and at least two barrier-like members (3), and further andoptionally a mooring cable (4) and/or an auxiliary cable (5), whereinsaid barrier-like members (3) are moored directly by using saidlongitudinal cables (1) and/or said lateral cable (7) or by using saidmooring cable (4) connected to each longitudinal cable (1) and/or saidlateral cable (7), so that the barrier-like members (3) are provided atan appropriate interval in the direction of the height of a mountainwith their longer dimensions substantially at right angles to thedirection of the height of the mountain, said base point (2) is providedon a slope of the mountain opposite the side of the mountain on whichsaid barrier-like members (3) are provided, and said longitudinal cables(1) are fixed to said base point (2) directly or indirectly via saidauxiliary cable (5) across a ridge of the mountain and are connected toeach other with said lateral cable (7).
 56. Amountain-landslide-preventive structure comprising at least twolongitudinal cables (1), a base point (2) constituted by a cable that iswound around a mountain, at least one lateral cable (7), and at leasttwo barrier-like members (3), and further and optionally a mooring cable(4), wherein said longitudinal cables (1) are fixed to said base point(2) and are connected to each other with said lateral cable (7), andsaid barrier-like members (3) are moored directly by using saidlongitudinal cables (1) and/or said lateral cable (7) or by using saidmooring cable (4) connected to each longitudinal cable (1) and/or saidlateral cable (7), so that the barrier-like members (3) are provided atan appropriate interval in the direction of the height of the mountainwith their longer dimensions substantially at right angles to thedirection of the height of the mountain.